A plurality of conventional wireless data communication technologies are as follows.
For example, many developers have conducted intensive research into a MIMO (Multiple-Input Multiple-Output) technique for increasing spectral efficiency (i.e., an amount of communication information for each unit time and each unit frequency) in a wireless communication field.
For example, there is almost no doubt that the IEEE 802.11 standard for WLAN (Wireless LAN) standardization adopts the MIMO technology in a task group (n).
Also, many developers are conducting research into a method for applying the MIMO technology to the fourth-generation mobile communication system to increase a transmission rate (also called a transfer rate).
The above-mentioned MIMO technology begins to extend/apply to the SDMA technology. The SDMA technology allows a single AP (Access Point) to simultaneously communicate with a plurality of UTs (User Terminals) using the same frequency signal.
Representative examples of the above-mentioned MIMO-SDMA technology are United States Patent Publication No. 2004-0252632A1, and a Japanese reference document entitled “Method for calculating MIMO/SDMA downlink weight using Rx antenna selection” published in The Institute of Electronics, Information and Communication Engineers Book B-5-230, filed by Nishimura Tosihiko, Takatori Yasusi, Ogane Takeo, Ogawa Yasutaka, and Osa Keizo.